Effect of solution chemistry on the surface charge of polymeric reverse osmosis and nanofiltration membranes

http://www.oocities.org/santanuparia/research/pdf/acis-04.pdf

A review on experimental studies of surfactant adsorption at the hydrophilic solid-water interface.

The performance (i.e., water flux and solute rejection) of a thin-film composite aromatic polyamide nanofiltration membrane and its relation to membrane surface charge (electrokinetic) characteristics were investigated. Membrane performance and streaming potential measurements were carried out as a function of pH for several solution chemistries, including an indifferent electrolyte, humic acid, and anionic and cationic surfactants. Performance results for the membrane were interpreted by relating the water flux and salt/ion rejection to the membrane charge characteristics. In the case of the indifferent electrolyte (NaCl), water flux and salt passage were maximal at the membrane pore isoelectric point (pH 5) primarily due to decreased electrostatic repulsion and increased pore volume (size) in the cross-linked polymer network. Ion rejection is directly related to the membrane pore charge and is attributed to co-ion electrostatic repulsion (exclusion). At low pH, negative rejection of protons was observed...

Relating Nanofiltration Membrane Performance to Membrane Charge (Electrokinetic) Characteristics

http://www.columbia.edu/cu/iucrc/IAB/May2007/NSF%20IUCRC%20Papers/Advances%20in%20adsorption%20of%20surfactants%20and%20their%20mixtures%20at%20solid-solution%20interfaces.pdf

Advances in adsorption of surfactants and their mixtures at solid/solution interfaces.

Adsorption of organic molecules on silica surface.

http://www.columbia.edu/~ps24/PDFs/Fluorescence%20Probe%20Studies%20on%20the%20Structure%20...%20Alumina%20Wate.pdf

Fluorescence probe studies on the structure of the adsorbed layer of dodecyl sulfate at the alumina—water interface

Emploi de pyrene et d'acide polyacrylique marque au pyrene comme marqueurs de fluorescence pour etudier les interactions entre l'acide polyacrylique et le bromure de dodecyltrimethylammonium

/pdf/fluorescence-probe-investigation-of-anionic-polymer-cationic-2q57nvhrp7.pdf

Fluorescence probe investigation of anionic polymer-cationic surfactant interactions

The conformations of a pyrene-labeled poly(acrylic acid) adsorbed at the water-solid interface were studied by using fluorescence of the pyrene excimer as an indication of the presence or absence of polymer strand coiling. It is found that adsorption from aqueous solution onto positively charged alumina is rapid and that the conformation of the polymer at the surface reflects the state of the polymer in solution prior to adsorption. In the case of high pH adsorption, the extended polymer (low excimer contribution) bound to the surface is not affected by lowering the pH of the solution. In contrast, when the polymer is initially adsorbed in coiled form (low pH), raising the pH of the solution partially leads to extension of the polymer on the surface. Binding to positively charged silica leads to a more extended conformation of the polymer which is relatively unaffected by the pH of the solution; that is, adsorption at high pH followed by a decrease in pH does not change the relative amount of excimer present.

Excimer fluorescence determination of solid-liquid interfacial pyrene-labeled poly(acrylic acid) conformations

Three nitroxide spin probes (5-, 12-, and 16-doxylstearic acid) were used to investigate the structure of sodium dodecyl sulfate (SDS) micelles and the interfacial layer between water and alumina formed by SDS (hemimicelles of SDS). It was found that whereas the rotational correlation times of the three probes differ in SDS micelles, the effective microviscosities of the probes are the same. In contrast, the microviscosity within the SDS hemimicelles varies according to the distance from the alumina surface: the nitroxide sees a more ordered environment as it is placed closer to the alumina. This represents the first report of variations in flexibility (microviscosity) within a hemimicelle. The science of the water-solid interfacial layer formed by adsorbed long-chain surfactants on solids has been studied extensively for its value in the fields of enhanced oil recovery,2 fl~tation,~ detergen~y,~ l ~brication,~ and microelectronics.6 Considerable experimental evidence is consistent with the postulate that such surfactants form localized aggregates (termed hemimicelles) on the solid surface.’ The evidence for hemimicelles has generally been indirect, and hemimicelle structure and dynamics have been inferred from measurements of bulk properties using such techniques as adsorption isotherms, {potentials, particle wettability, and heats of adsorption.8 Recently we reported the use of two types of molecular probes for use in spectroscopic investigations of the hemimicelle microstructure formed by sodium dodecyl sulfate (SDS) adsorbed on alumina. The first involved studies of pyrene and dinaphthylpropane fl~orescence,~ while the second involved the spin probe 16-doxylstearic acid (l), a stable nitroxide radical, for use with ESR spectroscopy.i0 The carboxylate functionality of this latter probe adsorbs on the positively charged alumina surface. Our results indicated that at pH 6.5 this probe aggregates mostly by itself on the surface at low SDS concentrations and forms cohemimicelles with the SDS at higher SDS concentrations. The relative anisotropy observed in an ESR spectrum is directly related to the rotational mobility of the probe, a term that can be correlated with the probe’s microviscosity.” Using this correlation, we were able to deduce that the environment within the SDS hemimicelle is relatively viscous. In both these studies of the microenvironment of the SDS hemimicelle, the data reported represent a single probe position within the hemimicelle (or a time average of many depths from the surface). Spin probes have been used extensively to study the microviscosity and micropolarity of membranes, multilayers, and micelles.12 In particular, doxylstearic acid spin probes have been useful in determining these parameters for different probe depths within phospholipid bilayers and micelles. Such studies have provided information on the orientation of the probes within the systems as well as information on the microenvironmental differences within the bilayer or micelle. In this communication, we wish to report the use of three doxylstearic acid derivatives, 16-, 12-, and 5-doxylstearic acids (1, 2, and 3, respectively) in

Variation in nitroxide probe chain flexibility within sodium dodecyl sulfate hemimicelles

A nitroxide spin probe is used to examine tbe pr~ of hcmimiceJle formation or the anionic surfactant sodium dcKiecyl sulfate (5DS) adsorbed on alumina b) ESR spectroscopy of the slurry. It is found that, at low SDS concentrations, the probe iuclf aurept5 <Xt he surface. As the 5DS ooncentration is raised such that 5DS hemimice1l5 fann, the probe aggregat5 are broken up, and tbe rQultin& ESR spectrum is ~istent witb the nitroxide bein& witbin the SD5 hemimicclles wIth a local Yisccaity of 120-165 cPo

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Papers

Fluorescence probe studies on the structure of the adsorbed layer of dodecyl sulfate at the alumina—water interface

Fluorescence probe investigation of anionic polymer-cationic surfactant interactions

Excimer fluorescence determination of solid-liquid interfacial pyrene-labeled poly(acrylic acid) conformations

Variation in nitroxide probe chain flexibility within sodium dodecyl sulfate hemimicelles

Use of a nitroxide spin probe to study the structure of the adsorbed layer of dodecyl sulfate at the alumina-water interface